The increased capabilities of unmanned airborne vehicles extends their deployment range from line-of-sight to well over-the-horizon distances. An unmet requirement for these vehicle systems is that they must be relatively inexpensive, have a high data rate, and provide for reliable over-the-horizon communications. Contemporary systems with these increased range capabilities inherently have limitations, such as a degradation in the reliability of communications and a performance vulnerability to natural and man-made interference. In fact, conventional radio links are compromisable to such a degree as to limit their associated systems' ability to perform a mission effectively. In addition, the conventional radio link systems also have an unfavorable tendency to broadcast the location of the mother launch vessel or installation. Various signal switching or signal modification techniques are added to try to limit the effectiveness of anticipated countermeasures; however, increased system complexity and a reduction of data rates are often an unfavorable tradeoff. So, the contemporary, conventional radio data links do not demonstrate an acceptable degree of practicality for use as a data link for weapons and unmanned autonomous vehicle reconnaissance systems.
The use of satellites for providing an extended over-the-horizon communications capability may at first appear to be the solution. However, this approach is less than completely satisfactory since the use of a satellite for a conventional radio link relay is expensive and may not always be available. A satellite's usable capacity might be limited to only priority communications so that applications such as weapons control or unmanned autonomous vehicle-launch platform systems need an alternate communications link. And, as with conventional radio data links, the satellite is vulnerable to naturally occurring and man-made interference.
Thus, a continuing need exists in the state of the art for a high data rate over-the-horizon communications capability between two or more platforms at rest or in motion, in the air or on the surface which includes a fiber optic data link operatively coupled to an RF data link by means of an interposed relay station, such as a parachute-borne or balloon-borne RF transmitter/receiver-optical fiber interface unit.